Lecture 2- DNAo antiparallelo Sugar-phosphate backboneo Nucleotide : sugar + Phosphate+ baseo Bases : pyrimidines (CUT) andpurines (AG) o DNA has 2’-deoxyribose (noOH), RNA has riboseo Nucleotides joined by covalentbond between 3’ C -OH and Pon 5’ C of next nucleotide – usetriphosphates in linking (lose PPi)o DNA wraps around histone proteins (positively chargednegativecharge of DNA neutralized), forming nucleosomes, which condensesinto chromatin fiber, forming a chromatido Sister chromatid vs. homologous chromosomes (#chromatids = #DNA helices)- Mendel (1866)- Griffith (1928)o Discovered transforming principleo Type IIR bacteria (nonvirulent) were transformed into Type IIISbacteria (S=smooth/slimy=virulent)- Avery, Macleod, McCarty (1944)o Transforming principle is DNA o Used protease and RNase, Type IIIS still presento Used DNase and only Type IIR present- Chargaff’s rule (1948)o # purines = # pyrimidines- Hershey and Chase (1952) o Phage genome is DNA , all other parts are proteino Radioactive label S35 and P32, only P32 has progeny that areradioactive- Watson and Crick along with Rosalind Franklin (1953)o DNA double helix structure- Fraenkel, Conrat, and Singer ((1956)o RNA can be the genetic material in some virusesLecture 3- Central Dogma: DNARNAprotein- Transcription : make mRNA form DNAo In nucleuso Uracil instead of thymineo RNA polymerase attaches to promotero In prokaryotes, the mRNA is translated without further processingo In eukaryotes, the mRNA is processed: introns spliced out, 5’ cap, 3’poly-A tailTranslation: make polypeptide from mRNAo In cytosol, on ribosomes (made of protein + RNA)o Codons read 5’3’ (codon = triplet of bases)o AUG = Start codon  Methionine (MET or M)o UAA, UGA, UAG = stop codonso Each tRNA carries specific aa and specific anticodon on other end(complementary to codon on mRNA)- Mutations :o Mistakes made in transcription/translation are not inherited,mistakes made in replication are inheritedo Changes made to aa inside the protein are most harmfulo Point mutation : change in one base pair (MAY lead to abnormalprotein)1. Substitution – missense (more common, wrong aa), nonsense(stop codon), or silent (same aa)2. Insertion/deletion – can cause frameshift = BADa. 3 base pair insertion/deletion will not lead to frameshifto Sickle cell disease : single point mutation changes entire Hb proteinconformation (gluval)—exposed hydrophobic surface regions withaggregate into filamentso Mutagen : physical or chemical agents that can cause mutationso spontaneous mutations can occur during replication, recombination,or repair- genotype = potential for certain phenotype (environment matters)Lectures 4/5- Meselson and Stahl – 1958 – showed that replication is semiconservativeo Start with 15N, and then transfer to 14N medium and replicateo After centrifugation, there will be heavy, medium, or lighto 6 LL and 2 HL chains  semiconservative- Nucleotide selection, DNA proofreading, mismatch repair- At centromere: kinetochore proteins and spindle microtubules- Spindle microtubules : made of tubulin subunits-lengthen and shorten at either + or – end- Mitosis : at metaphase sister kinetochores orient toward different poles, andcohesion keeps chromatids together – at anaphase breakdown of cohesion byseparase allows sister chromatids to separate- Meiosis : at metaphase I cohesion along chromosome arms holds homologstogether at chiasmata – at anaphase I cohesion along chromosome armsbreak down allowing homologs to separate, but cohesion at the centromereis protected by shugoshin – at anaphase II shugoshin is degraded so cohesionat the centromeres breaks down allowing sister chromatids to separate- Chromosomes duplicated in S phaseMITOSIS- Prophase o Centrosomes separate to opposite sides of cell and stretchmicrotubuleso Nucleus condenses- Prometaphase o Nuclear envelope broken downo Chromosomes condensed completelyo Centrosomes at opposite ends of cellso Microtubules stretched across- Metaphase o Metaphase plate - chromosomes line up (centromeres in line)- Anaphase o Microtubules shorten and pulls sister chromatids toward separatesides- Telophase and Cytokinesis o Chromosomes de-condense, nuclear envelope reformso Daughter nuclei form at opposite ends of cello Cytoplasm pinches in (cleavage furrow) - ANIMAL CELLS ONLYPLANT CELL division requires a cell plate, which forms a new cell wall- Mitotic spindle: apparatus of microtubules- Centrosomes : aster and kinetochore microtubules (spindle)o where spindle arises (microtubule organizing center)o only some of the many microtubules will attach to kinetochore ofchromosomes and move the chromosomes to the metaphase plateo in anaphase, kinetochore microtubules shorten = depolarimerize(shorten at ends by sister chromatids)1. Kinetochore microtubules: attach to kinetochore and shorten to separate sisterchromatids2. Nonkinetochore microtubules: continue to lengthen, overlap and push againsteach other which elongates cells-from opposite poles3. Aster: attach to plasma membrane and anchor spindles at polesMeiosis versus Mitosis- 3 events in Meiosis: %1. Synapsis and crossing over-non-sister chromatids exchangesynapsis is the pairing of homologous chromosomes during the meiotic phase of celldivision%6.2. Tetrads on metaphase plate in Meiosis I%6.3. Separation of homologous chromosomes in Anaphase I-haploid cells with sister chromatids attachedSummary of Mitosis vs. Meiosis in Animal CellsMitosis MeiosisNumber of divisions 1 2Synapsis? no yesNumber of daughtercells2 4Are daughter cellsdiploid or haploid?diploid haploidAre daughter cellsidentical to parent cell?yes noAre daughter cellsidentical to each other?yes noGENETIC VARIATION%6.1. Independent Assortment%Each pair of maternal and paternal homologues is sorted independently of otherpairs-50% that gamete will get either paternal or maternal chromosome2n where n = haploid #223 = 8 million possible combinations%2. Crossing over%6.Produces recombinant chromosomes (contain genes from each parent)%3. Random fertilization%6.Fusion of 2 gametes is random%6.Total # of chromosome combinations for diploid zygote is product of variation foreach gamete223 x 223